1. Technical Field
The present invention relates to the field of positive-displacement piston pumps.
An advantageous application of such a pump relates to the supply of rubber to an extruder intended to form a profiled element for manufacturing a vehicle tire. Such a pump can, of course, be used for all kinds of viscous and liquid products.
2. Related Art
Conventionally, a positive-displacement or volumetric pump comprises a product metering piston mounted in a cylinder of the pump body forming a metering chamber so as to slide, and means for actuating the piston, for example a cam in contact with one end of the latter.
One type of volumetric pump also comprises a dispensing plug mounted so as to rotate inside a sleeve of the pump body in order to place the metering chamber alternately into communication with an intake chamber and an exhaust chamber of the sleeve, by way of an orifice provided in the thickness of said sleeve.
To this end, first and second groups of grooves are formed on the outer surface of the plug and are arranged so as to pass in front of the orifice in the sleeve during the rotation of the plug so as to place the metering chamber successively into communication with the intake chamber and then with the exhaust chamber.
Thus, the pumped product flows from the intake chamber to the metering chamber, and then from this metering chamber to the exhaust chamber, passing through the same orifice. For more details relating to a pump of this type, reference may be made for example to the patent application EP-A1-0 604 888.
With such a pump, it is necessary to provide a radial functional clearance between the outer surface of the rotary plug and the bore of the sleeve of the pump body holding the plug. Moreover, this clearance tends to enlarge with the radial friction and wear that exist between the plug and the sleeve. As a result, leaks of the product present inside the intake chamber directly towards the exhaust chamber can occur, notably when the pumped product is rubber or some other viscous product that has low viscosity.
Furthermore, such leaks can also exist along the outer surface of the plug, circumferentially between the intake grooves and the exhaust grooves in the event of this outer surface being worn, for example by scratches, abrasion, etc., which can be caused by contaminating particles contained in the product to be pumped.
With such uncontrolled flows of product between the intake and exhaust grooves of the plug and/or between the plug and the sleeve of the pump body, the flow rate of the pump can be irregular.